Posted by
Edward H Russell on
Jun 08, 2020; 7:29pm
URL: http://elecraft.85.s1.nabble.com/CW-rise-time-setting-tp7661876p7661886.html
I suppose shaping of the curve corners removes harmonics introduced by the abrupt transitions, allowing an accelerated ramp inbetween. But does this really reduce the total rise time to 2.5ms? It seems that the softening process must take some time. Wish I had a K3 here to scope against other radios. Anything published out there?
Ed / w2rf
From: Alan Bloom <
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Sent: Monday, June 8, 2020 3:15 PM
To: E.H. Russell <
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Cc: 'Elecraft Reflector' <
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Subject: Re: [Elecraft] CW rise time setting
In the "good old days" key shaping was done simply by adding a capacitor to the key line or equivalent. That results in an exponential rise and/or fall time, which is not optimum, so the time constant had to be set pretty slow to avoid key clicks. Typically 5-10 ms. 10 ms results in "mushy" keying, especially at high CW speeds.
Raised-cosine key shaping is close to optimum and is easy to implement with a DSP. It allows faster rise/fall times without key clicks. I assume Elecraft is using something like that.
Alan N1AL
On 2020-06-08 12:51, E.H. Russell wrote:
I'm used to CW rise times in th 4-7ms range. Is this 2.5ms arrived at by a
different metric? Is the curve added by sigmoidal shaping somehow excluded
from the measurement?
Ed / w2rf
-----Original Message-----
From:
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Behalf Of Richard Stutsman
Sent: Monday, June 8, 2020 1:31 PM
To: David Gilbert <
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Cc: Elecraft Reflector <
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Subject: Re: [Elecraft] CW rise time setting
Yes, I would regard a 2.5 msec rise time (using appropriate sigmoid
shaping) to probably be ideal, in which case I would have no desire to
modify or shorten it. I'll bet it will sound even better than a Drake or a
Ten-Tec!
I hereby withdraw my previous request/opinion.
Rick N6IET
On Mon, Jun 8, 2020 at 10:27 AM David Gilbert < <mailto:
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You don't need to generate clicks to have a crisp CW tone. Elecraft
uses a pretty much optimally shaped waveform (some version of a cosine
function) and if I remember correctly the rise time is only about 2.5
msec, although I could be wrong about that last part. And while you
may be careful not to use short rise/fall times when the band is
active, in the past there have been folks on the contesting reflector
who openly admitted they purposely generate clicks by shortening the
rise/fall times to give themselves elbow room. I will always
appreciate that Elecraft doesn't give those miscreants the means to
pollute the band.
73,
Dave AB7E
On Mon, Jun 8, 2020 at 9:23 AM Richard Stutsman <
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I for one would like to have some control over the rise/fall times.
You want the cleanest (narrowest) of CW signals when operating on a
crowded band or in a contest - unless you're a rare DX station. Most
of my operations are 22wpm rag chews on very uncrowded bands. We're
often the only discernible signals on an entire CW band. And
conditions are often noisy with deep QSB. Why not allow those of us
operating in those circumstances to shorten the rise times a bit,
which makes it easier to copy in noisy conditions, when any close-in
clicks or thumps aren't going to bother anybody? Copying a 'soft'
weak CW signal is like trying to read a 'crisp' signal that's an
entire S-unit weaker, IMO.
My TS-590sg let's me do that, and I love it!
Will the K4 sound as good as a Drake T4C? (Just askin'.)
Rick N6IET
N4ZR wrote:
Will the K4 have options for setting CW rise and fall times...?
Hi Pete,
Probably not. We've always been very careful to ensure our rigs
have an exceptional clean, click-free CW signal. (Third-party
testing bears this
out.) Minimizing the bandwidth requires a very specific rise/fall
time
and
a hand-crafted sigmoidal shaping function in DSP.
Colonel Sanders closely guards his fried chick recipe, Mrs. Fields
won't reveal what's in her chocolate-chip cookies, and only
selected firmware monks--sworn to secrecy--are privy to Elecraft's
keying envelope coefficients :) 73, Wayne N6KR
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